[Discuss] what are pros/cons of different (Linux) filesystems for use with SMR (shingled) hard drives?

[kentborg at borg.org (Kent Borg)]

On 11/13/20 2:34 PM, Bill Bogstad wrote:
> An external USB drive that I use solely for full and incremental
> backups is developing bad blocks. For pricing reasons, I'm going with
> a new drive which uses SMR for recording.

I might be doing that and don't know it. Are the new portable 5TB WD 
USB-C affordable disks disk-managed SMR? If so, I am. (Before that, a 
sequence of old "super speed" USB disks and somewhat smaller capacity, 
depending on purchase date.)

I wondered why, after I am done with the backup, I can feel the disk 
vibrating, still doing something for some time later. I do note the 
USB-Cs are shorter in this than were the previous models. Maybe that was 
the disk managing itself.

> I backup with rsync and a
> hard link tree  for incrementals which means that file data is
> typically not overwritten at the file level.  Metadata of old files
> changes when a hard link in a new incremental is made to the
> preexisting file.   A

That I *am* doing and have been doing for sometime. (rsync and 
--link-dest is great!) And because these disks are affordable I 
ping-pong between multiple disks, kept in different locations.

Because I litter these in various locations, I encrypt them; luksFormat 
the whole disk, and then format with XFS.

Donno why I chose XFS, seemed like a good idea back when.

This has worked well, I have not only done backups but also done 
"restores" (for copying my data to a new computer, more than once, only 
a couple times grabbing a specific old file).

The whole system has worked great, I really like that every time I do a 
backup I am smoke testing that the disk still significantly works and 
will ~likely~ be able to do a restore. (I would like a Linux file system 
that is error checked, but last I looked I didn't see a good option for 
that.)

It is nice that the backup directly mountable, making the "restore time" 
extremely short if I can do what I need directly off the disk.

That last couple disks (the USB-C) I have been a good camper and written 
the entire disk with high quality random data before luksFormat and mkfs.

> re there any things I should watch out for this
> use case?   Particular filesystems that are either good or bad for SMR
> drives?  I obviously want the system to be reliable, but I doubt that
> making the system rewrite shingles over and over again due to frequent
> updates to the same disk blocks is good for the longevity of the
> drive.  Any info/opinions appreciated.

A disk managed SMR (if done well) is not going to rewrite the shingles 
that much, it is going to remap things to avoid that. Isn't it?? But the 
remapping isn't free, some usage patterns are going to stress it. I do 
my incremental backups every few days at most, and even then I am 
rotating that across more than one disk, so each backup is significant 
in size, the ratio of meta data rewrite to new data isn't going to be 
that high. If disk managed SMR firmware can work with any usage pattern, 
I think the write-once nature of this backup scheme should be pretty 
friendly.

-kb